Monotremes
Short-beaked echidnas and platypuses (Ornithorhychus anatinus) are opportunistic foragers. Recent research utilising DNA metabarcoding has revealed a wider variety of invertebrates in their natural diets than previously thought (Augee et al.
2006; Hawke et al. 2022; Perry et al. 2022; Spencer and Richards 2009; Sprent and Nicol 2016).Energy requirements, prey selection and intake may be affected by a variety of factors such as life stage, ambient temperature and activity level. Although platypus BMR is higher than that of short-beaked echidnas, it is still only half that expected for similarly sized eutherian mammals (Augee et al. 2006; Holz 2015 and references therein) (Table 14.2). Platypuses can feed for up to 12 h, consuming 13-28% of their bodyweight daily, while echidnas ingest ~5% bodyweight daily (Holz 2015). Reduced foraging-related activity may result in significantly lower maintenance energy requirements for managed v. free- ranging echidnas (Barker et al. 2016; Stannard et al. 2017). However, echidnas may experience heightened energetic demands seasonally or during periods of growth. The juvenile stage may be an energetically demanding life stage for monotremes in general, but protein, and specifically, sulphur-containing amino acid (SAA) requirements for spine growth, may also be driving consumption in echidnas (Shaw 2023). Female platypuses will also increase energetic demand during lactation, consuming up to 100% bodyweight of higher energy prey, while echidna requirements do not change (Bethge et al. 2003; McLachlan-Troup et al. 2010; Klamt et al. 2016; Nicol and Andersen 2007).
Energetic demands and prey choice may also increase during higher environmental temperatures as mono- tremes appear more susceptible to hyper- v. hypothermia (Barker et al. 2016). Diets must account for increases in BMR of ~10% for every 1°C increase over Tb (31.7°C in platypuses and 29.5°C in echidnas).
Monitoring bodyweight and body condition regularly and adjusting amount offered is important as animals may lose weight rapidly as demands increase.Short-beaked echidna and platypus digestive morphology and physiology has been described (Booth and Connolly 2008; Middleton 2008; Spencer and Richards 2009; Krause 2011; Holz 2015) (Fig. 14.3). Although the mono- treme GIT morphologically resemble the carnivore (Fig. 14.3), recent studies on free-ranging and short- beaked echidnas in managed care suggest that functionally and physiologically a foregut-fermenting herbivore animal model may be more appropriate for some insectivores (Shaw et al. 2017; Tong et al. 2017) (Table 14.1). Unlike typical carnivores, echidnas have a single chambered stomach which is completely lined with keratinised squamous (non-glandular) cells that are closely associated with a large population of uniform coc- coid bacteria like the gut microbiome composition of ruminants and ants and capable of microbial fermentation (He et al. 2013; Abdul Rahman et al. 2016; Tong et al. 2017). These similarities relate to the microbial requirement for digesting plant material such as pre-digested wood fibre in termite mounds and the gut contents of invertebrate prey.
Firmicutes, Proteobacteria, Fusobacteria and Bacte- roidetes are among the dominant phyla in faecal samples from short-beaked echidnas and platypuses which include bacteria generally associated with fibre fermentation in herbivores (Perry et al. 2022; Buthgamuwa et al. 2023; Dungan and Thomas 2024). Differences in the microbiomes of managed and free-ranging myrme- cophages have been attributed to differences in diet and the ingestion of soil microbes from around ant and termite nests in situ (Delsuc et al. 2014). Echidnas are reported to eat large amounts of soil, which may aid in digestion, be a source of minerals and improve faecal consistency. However, symbiotic bacteria found in termite mounds, soil and in prey items may play a more significant role in digestion, including providing chitinase to increase availability of nitrogen bound in the exoskeletons of prey (Vaaje-Kolstad et al.
2009; Kohler et al. 2012; Delsuc et al. 2014; Abdul Rahman et al. 2016).Stable isotope analysis of both free-ranging platypus fur and echidna spines indicates a trophic level akin to herbivores (δ15N values ~7‰), hinting at the inclusion of plant material indirectly in their diets (Klamt et al. 2016; Shaw et al. 2017). A significant proportion of plant DNA (likely ingesta of prey species) has also been identified in free-ranging echidna and platypus faecal samples (Perry et al. 2022; Dungan and Thomas 2024).
Short-beaked echidna saliva has a pH of ~8, as does the empty stomach. This may act as a buffer against acid produced during microbial fermentation, which causes the stomach pH to drop as low as 4.5 after feeding (Shaw et al. 2017). In echidnas suffering dysbiosis this pH balance may not be maintained, resulting in gastritis. Transfaunation from healthy echidnas will potentially encourage growth of a healthy microbiome in compromised individuals (Shaw 2023). A general transfauna- tion protocol is outlined in Table 14.3.
A successful echidna diet promotes proliferation of beneficial bacteria, inhibits growth of harmful bacteria, yeasts and fungi and meets basic nutrient recommendations (Box 14.1). Short-beaked echidnas can be maintained and bred on in-house mixes and/or a commercial diet (Shaw 2023). Termites have very high levels of copper, zinc, iron and vitamin A, so short-beaked echidna requirements may exceed those of other species but should still be within known limits for domestic animal models to avoid toxicity (Table 14.1). In-house mixes tend to have lower than recommended levels of calcium, copper, zinc and vitamin E and some may have excessive levels of vitamins A and D (Scheelings and Haynes 2012; Shaw 2023; Stannard et al. 2017). Concentrated liquid avian vitamin supplements should be avoided to reduce risk of vitamin toxicosis. These nutrients have several functions, including critical roles in reproduction. High dietary vitamin D levels have resulted in elevated serum 25(OH)D concentration in adults and metastatic calcification in puggles hand-reared on echidna-specific milk replacer (Scheelings and Haynes 2012; Scheelings et al.
2017). It is possible that the low calcium levels in these diets reduced the risk of tissue calcification in adult echidnas fed diets high in vitamin D and that young animals are more susceptible to toxicity. If echidnas are able to absorb calcium without the need for vitamin D, then available milk replacers may still contain excessive calcium and the risk of hypervitaminosis during handrearing must be considered.Echidna puggles should ideally be mother-reared, but if orphaned, appropriate milk replacers must be used, ensuring minimal lactose, and high milk solids and protein. Echidna milk oligosaccharides likely play prebiotic roles, necessitating further study for improved milk replacer formulations (Mandal et al. 2015; M Power pers. comm.; Sela and Mills 2010). The adult short-beaked echidna foregut is a fermentation chamber that becomes acidotic when fed highly digestible carbohydrate (Tong et al. 2017). Offering milk to adult short-beaked echidnas should be avoided to reduce risk of gastritis and subsequent scarring that affects digestive capabilities throughout life (see Chapter 29).
Table 14.3. Transfaunation/Faecal Microbiota Transplantation (FMT) procedure
| Step | Procedures |
| 1. Collect donor faeces | Collect a small amount (< 5 g) of fresh faeces from a healthy donor. Donor may be a rescued wild animal (e.g. hospitalised due to physical injury) or a healthy zoo-housed adult. For hand-reared zoo-bred animals the dam (if available) is an ideal donor. |
| 2. Screen donor faeces | a. Screen donor faeces for pathogens, particularly parasites that may pose a risk to the recipient. The presence of parasites does not necessarily exclude a sample from use (e.g. early exposure to coccidia, normally found in free- ranging healthy echidnas, may be beneficial; see Chapter 30). b. The sample can be held refrigerated at 4°C for 24-48 h while screening is being completed. |
| 3. Hindgut fermenters only (wombats, koalas, possums) | a. Collect several fresh faecal pellets from approved donor. Note: in species with a high degree of caecal fermentation (e.g. possums and koalas), caecal pellets are preferred but rarely available. b. Soak whole pellets in lukewarm distilled (or previously boiled) water for 1 h (just enough to cover pellets). Mucous coating on pellets will swell (this portion is most like the caecal microbiome). c. Gently stir or agitate the mix to loosen the mucous coating. d. Syringe off supernatant (mucous) and continue to step 4c. |
| 4. Prepare faeces | a. Mix faecal sample with 2-5 ml water or saline. b. Filter faecal solution (through gauze or sieve) to remove large particles and collect the liquid. c. Discard solid particles and collect the supernatant into a sterile container. d. Ideally made fresh daily for optimal results but can be refrigerated at 4°C for up to 48 h. |
| 5. Administer | The following methods may be used to administer the supernatant: a. Orally - the supernatant (volume chosen is empirical and a reasonable volume for the size of animal can be used) is added to a small amount of food. One 'dose' may be enough but 3 to 9 consecutive days is preferable (Blyton et al. 2019; DePeters and George 2014). If the animal accepts this without issue on the first day, the volume can be increased on the second and third day. For hand-reared animals, repeat in 21 days. Administering the supernatant in an acid-resistant capsule may help protect the microbes in species with a low gastric pH (Blyton et al. 2019). Tubing may need to be done under anaesthesia (e.g. echidnas), so frequency may need to be adjusted based on the animal's health and tolerance of frequent anaesthetics. If gastric tubing is being performed in an echidna it is beneficial to obtain a gastric sample before FMT to characterise the stomach microbial flora and before subsequent FMT procedures to assess efficacy of treatment.b. Colonic - in some circumstances depending on the condition being treated, species and patient, FMT can be administered into the colon. |
| 6. Feed microbes | It is important to promote the growth of the appropriate microbial population. For example, in herbivores, if high fibre feed such as ground browse, Emeraid® Herbivore (Lafeber Co, Cornell, IL, USA) or Oxbow IC Herbivore (Oxbow Animal Health, Omaha, NE, USA) was not used in step 5a, then offering after FMT will help support and establish the new microbial population. |
Box 14.1. Recommendations for formulating diets for short-beaked echidnas (Tachyglossus aculeatus) in managed care
• Diets should be balanced to contain nutrient levels that meet average requirements and not exceed tolerable limits for model species until species-specific recommendations can be determined
• Highly fermentable carbohydrates (e.g. glucose, fruit, dairy - previously used to increase palatability and intake) should not be used in adult diets
• One or more fibre sources should be added e.g. bran, wheat germ, cellulose
• Access to termites, termite mounds (and/or soil from around termite mounds) is encouraged to regularly inoculate the gut and promote a natural microbiome
• Highly concentrated, liquid avian supplements must not be used as they have excessive fat-soluble vitamins A and D and are not formulated for use in mammalian diets
Complete nutritional analysis of free-ranging platypus prey items is not available therefore providing a variety of prey items is the best way of providing adequate nutrition (Table 14.4). Yabbies (Cherax destructor), earthworms (Lumbricus spp.), maggots and fly pupae (Musca domes- tica), blackworms, and ghost or glass shrimp (Paratya australiensis) are readily accepted by platypuses in managed care. Although whole live prey may be difficult to provide, it is preferred as no additional supplementation should be necessary to balance the diet. Platypus and echidna nutrition requires further research to ensure the managed care diets meet requirements at all life stages.
5.